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Journal of Natural Products Vol. 4 7 . No. 3,pp. 497-503, May-Jun 1984
MICROBIAL TRANSFORMATIONS OF NATURAL ANTITUMOR AGENTS, 25. CONVERSIONS OF 3-KETOAPHIDICOLIN JOHN
IPSEN and JOHN P. ROSAZZA*
Division of Medicinal Chmistv and Natural Products, College of Phannary, University oflmoa, Iowa City, IA 52242 ABSTRAcT.-Microbial transformation experiments were conducted using 3ketoaphidicolin ( 2 ) as a starting material. Metabolites were isolated by solvent extraction and chromatography, and structures were elaborated by cmr and pmr spectroscopy, ms, and ir analyses. Several microorganisms provided metabolites in excellent yields, including 3-epiaphidicolin (4), 6P-hydroxy-3-ketoaphidicolin( S ) , and 19-nor- 16,17-dihydroxyaphidicolan3-one (6).The last compound is formed via oxidation of the primary alcohol functional group at position 18 to the corresponding P-keto acid derivative which spontaneously decarboxylates. This reaction is analogous tp the metabolic demethylation of sterol intermediates. Each metabolite was tested for antitumor activity in the P-388 leukemic test system, and in the 6C63 1 colon tumor model system. None of the compounds were active in vivo, and all were less active than aphidicolin in the in vitro P-388 test system.
3a, 16,17,18-Tetrahydroxyaphidicolane(aphidicolin, 1) is a novel antitumor diterpene derivative produced by a species of Cephalosporium (1) and of Nigrosporum (2). Microbiological transformations were successfully used to produce six major derivatives of aphidicolin (3). These included acylated, hydroxylated, epimerized, and dehydrogenated microbial products, all of which were obtained in good yield. One of the major metabolites described in our previous work was 16,17,18-trihydroxyaphidicoIan-3-one (2). Because the 3-ketoaphidicolin analog could be prepared in high yield, further biotransformation studies were performed using 2 as substrate. This report describes the production, isolation, and characterization of metabolities formed from 2 by microbial transformation. (See Figure 1.) OH
FIGURE1. Structures of aphidicolin (1)and microbial transformation products. Compound
1 2
3 4 5 6 7
R, a-OH =O a-OH P-OH =O =O a-OH
R* CH,OH CH20H CH20H CH20H CH,OH CH3 COOH
R4 H H P-OH H P-OH H H
EXPERIMENTAL GENERAL EXPERIMENTAL PROCEDURES.-Melting points were obtained in open-ended capillaries and are uncorrected. Ir spectra were obtained in KBr discs with a Beckman Model 4240 spectrophotometer. N m r spectra were taken in pyridine-D,, CDCI,, or C6D, using TMS as an internal standard. Pmr
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and cmr spectra were taken on a Briiker HX-90E instrument, and low resolution mass spectra were obtained on a Hewlett-Packard 5985 gclms system with a direct inlet probe. High resolution mass spectra were obtained through the Midwest Center for Mass Spectrometry, The Chemistry Department, University of Nebraska, Lincoln, NE. CHROMATOGRAPHY.
